850 running reach w/no codes?

adrian222 · Post by **adrian222** » 25 Jan 2005, 10:45

I purchased a 1996 non-turbo automatic Volvo 850 (157k) a year ago. I have run across a problem, the car runs fine when cold but after 3 min at any speed is starting running rough and expel black smoke on tail pipe, I have no codes or check engine light on,If I wait for a few minutes, and I started again it is fine again for 3 min but the condition returned at precisely same interval of time. Gas mileage is really bad. The car is running reach but no codes??
There is no warning that the engine is about to cut off and it has the stabile idle around 850-900. I have taken the car to two different mechanics with no success. I have new(bosch) O2 sensor/front, spark plugs, new rotor and cap, new flame trap, cleaned idle motor, clean/new air filter and good battery. I could not find any vacuum leaks. Question is can the back O2 sensor cause this, it is not involved in mixture process?
Before all this happen I have the trany flushed with synthetic oil at the transmission garage. I had that the ABS light on the dash on before and it is still on but I do not see any relation.
Do you all have any idea what the problem could be???
Thanks Adrian

UncleBoost · Post by **UncleBoost** » 25 Jan 2005, 12:51

had the same problem but my idle would race away to hell...
try disconnecting your TEMP SENSOR and see if that makes a difference.
Does your Temp gage work?
Just try that and let the board know what happens.

Post by **dosbricks** » 25 Jan 2005, 12:55

Did you check the little vacuum elbow down on the passenger side end of the intake manifold (hard to see and even harder to get to). This line comes from the PCV system and oil contamination can cause the rubber to soften an colapse. That was the cause of my `96 running rich with no codes, although I didn't have any exhaust smoke. Also, I believe it caused the early demise of my O2 sensors.

adrian22 · Post by **adrian22** » 25 Jan 2005, 14:25

yes i did all you sugested,I have no visible vacum leaks, and I disconected temp. sensor,still same condition.When I disconected the temp. sensor the fan start running and did not stop even I stoped the engine and removed ckey from ignition!.I had to reconect sensor and restart car to stop the fan...
i was wandering if there is any test I can do in order to check vacum presure?

Jot · Post by **Jot** » 25 Jan 2005, 14:43

Did you double check the O2 sensor as to being the correct one. I have bought and installed the wrong one and ended up blowing carbon out the tailpipe mpg dropped to 15 . I did get a code for running rich along with an O2 voltage out of specs